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perf: override GOMAXPROCS to use all available CPUs #215

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perf: override GOMAXPROCS to use all available CPUs #215

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7 changes: 7 additions & 0 deletions cmd/cachew/main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,13 @@ type CLI struct {
}

func main() {
// Override GOMAXPROCS: container environments may set it to a low value
// (e.g. 2) based on cgroup CPU limits. With few OS threads available, the
// Go scheduler can't run the zstd decoder, tar reader, and file-write
// goroutines concurrently — they time-slice, and the pipeline stalls.
// Using all available CPUs lets all goroutines actually run in parallel.
runtime.GOMAXPROCS(runtime.NumCPU())

cli := CLI{}
kctx := kong.Parse(&cli, kong.UsageOnError(), kong.HelpOptions{Compact: true}, kong.DefaultEnvars("CACHEW"), kong.Bind(&cli))
ctx := context.Background()
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8 changes: 8 additions & 0 deletions cmd/cachewd/main.go
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Expand Up @@ -8,6 +8,7 @@ import (
"net/http"
_ "net/http/pprof" //nolint:gosec
"os"
"runtime"
"strings"
"time"

Expand Down Expand Up @@ -53,6 +54,13 @@ type CLI struct {
}

func main() {
// Override GOMAXPROCS: container environments may set it to a low value
// (e.g. 2) based on cgroup CPU limits. With few OS threads available, the
// Go scheduler can't run the zstd decoder, tar reader, and file-write
// goroutines concurrently — they time-slice, and the pipeline stalls.
// Using all available CPUs lets all goroutines actually run in parallel.
runtime.GOMAXPROCS(runtime.NumCPU())
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@chatgpt-codex-connector chatgpt-codex-connector Bot Mar 23, 2026

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P1 Badge Avoid bypassing quota-aware GOMAXPROCS defaults

Calling runtime.GOMAXPROCS(runtime.NumCPU()) here overrides both Go 1.25’s container-aware default and any operator-provided GOMAXPROCS value, which can over-subscribe CPU in quota-limited containers (for example, a pod limited to 2 CPUs on a 64-core node) and cause cgroup throttling/latency regressions under load; the same pattern is also introduced in cmd/cachew/main.go. Please keep the runtime default (or gate this behind an explicit opt-in) so deployments that rely on CPU limits are not penalized.

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var cli CLI
kctx := kong.Parse(&cli, kong.DefaultEnvars("CACHEW"))

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